Microstructured pattern inspection method

ABSTRACT

The edges of the reticle are detected with respect to the microstructured patterns exposed by the stepper, and the shapes of the microstructured patterns at the surface and at the bottom of the photoresist are detected. The microstructured patterns are evaluated by calculating, and displaying on the screen, the dislocation vector that represents the relationship in position between the detected patterns on the surface and at the bottom of the photoresist. Furthermore, dislocation vectors between the microstructured patterns at multiple positions in a single-chip or single-shot area or on one wafer are likewise calculated, then the sizes and distribution status of the dislocation vectors at each such position are categorized as characteristic quantities, and the corresponding tendencies are analyzed. Thus, stepper or wafer abnormality is detected.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/587/956 filed 02 Jun.2004, which is a continuation of application Ser. No. 10/389/882 filed18 Mar. 2003, now U.S. Pat. No. 6,765,204, which is a continuation ofapplication Ser. No. 09/684,469 filed 6 Oct. 2000, U.S. Pat. No.6,573,499.

The present invention relates to microstructured pattern inspectionmethod, particularly, to a method of inspecting the microstructuredpatterns, such as contact holes and linear patterns, that are formed onthe semiconductor wafers with the photolithography that uses an opticalexposure apparatus such as a stepper.

In the manufacture of semiconductors, photolithography is used to formpatterns on semiconductor wafers. The formation of these patterns mostcommonly uses the reduction project alignment method that applies anapparatus in which a reticle formed by enlarging the circuit patternsfor several chips is used for reduction projection alignment(hereinafter, this apparatus is referred to as the stepper). In thereduction projection alignment method using the stepper, a reduced imageof the mask pattern of the reticle is exposed to light so as to beprojected and formed on the photoresist coating of the wafer, with theresult that a resist pattern, a copy of the reticle mask pattern, isformed on that wafer by processing chemically the photosensitizedphotoresist coating. The patterns for several chips that have beenformed on the reticle can be copied with a single shot (exposure). Thisprocedure is “stepped and repeated” to copy more such patterns on thewafer.

An example of forming contact holes on the insulating film of the waferis described below. First, a photoresist coating is formed on theinsulating film. Next, the photoresist coating undergoes exposure usinga reticle provided with a pattern of contact holes of the design sizeand arrangement, and then undergoes chemical processing. After this,contact hole patterns passing through the insulating film can be formedon the wafer by performing processes such as etching, and in thisetching process, the photoresist coating that has been created bycopying the required pattern functions as a mask.

To ensure that the stepper forms patterns on the wafer as describedabove, the microstructured patterns on the dimensionally enlargedreticle must undergo reduction projection alignment on the wafer throughprojection optics. The surface and bottom of the exposed layer(photoresist coating) of the patterns that have been exposed to light inthe reduction projection alignment process occasionally differ in size,shape, position, and other factors.

The first main cause of these differences is a combination of defects inthe wafer material and defects in the workmanship of the substanceexposed to light on the wafer, such as a resist. The warping,distortion, deflection, and the like, of the wafer itself can occurduring its manufacture or according to the subsequent elapse of time orthe particular ambient environmental conditions such as temperature, andthese defects affect optical interference. The shapes of the patternsformed will also be affected by the nature of the substance to be usedas a resist, and by the resist coating thickness, coating status, andother factors. Such deviations (from design specifications) in terms ofthe forming positions and dimensions at the exposed surface and bottomof the microstructured patterns due to the characteristics of theexposed substance (hereinafter, these deviations are collectively called“dislocations”) are usually distributed over a wide range in a specificarea of the wafer, and with a fixed tendency.

The second main cause is such insufficiency in the performance of theoptics used in the stepper as schematized in FIG. 2. As shown in FIG. 2(a), no problems occur in the vicinity of the reticle center. As shownin FIG. 2 (b), however, if light is emitted obliquely to the surface ofthe wafer, lens aberration, such as astigmatism or comatic aberration,will occur at the edges of the reticle. Dislocation due to suchaberration mainly appears within a single-shot area, radially from itscentral position and with a fixed tendency.

The third main cause is a defect in the nature of the optics of thestepper, that is to say, a shift in focal position (defocusing), whicharises from the fact that the lenses in the optics used for exposuresuffer deformation due to the heat generated during exposure (this eventis called “lens heating”).

The fourth main cause is a defect in the performance of the optics ofthe stepper. If the optics of the stepper has any inclined parts such aslens, since the emitted light enters laterally, the exposure patternwithin a single-shot area skews in a fixed direction.

Differences between the design specifications and actually formedpatterns are mainly caused by the four factors described above. Thefirst problem resulting from these differences is that dislocationoccurs between the patterns that were formed on the surface and bottomof the photoresist. Similarly, there also occurs misalignment withrespect to the pattern in the lowere layer or upper layer of theinsulator, due to the axial and position offsets between the designspecifications and actually exposed patterns. Axial or position offsetsin contact hole patterns reduce the area of the hole, thus increasingelectrical resistance, and finally leading to deteriorated semiconductorperformance. In some cases, the semiconductor loses electroconductivity,which is a critical defect in the semiconductor device itself.

With respect to these problems, at present, exposure accuracy at thebottom area of the microstructured patterns is usually evaluated bycalculating the area of the bottom. However, there is no establishedmethod for evaluating quantitatively the optics of the stepper, thewafer, or the like, from the quantity or direction of patterndislocation or from these factors.

SUMMARY OF THE INVENTION

The present invention is therefore intended to provide a method ofevaluating each microstructured pattern of a semiconductor bycalculating as a dislocation vector the relationship in position betweenthe surface and bottom of the photoresist on the microstructuredpattern. The present invention is also intended to provide a method ofevaluating exposure accuracy quantitatively on a single-shot,single-chip, or wafer-by-wafer basis, or a method of evaluating eachsection of the pattern exposure system, detecting abnormality, andissuing a related warning.

During microstructured pattern evaluation based on the presentinvention, the formation status of the patterns on the surface of theexposed layer (hereinafter, simply called the surface layer) and at thebottom of the exposed layer (hereinafter, simply called the bottomlayer) and the relationship in position between the surface layer andthe bottom layer are analyzed, then the relative dislocation betweenboth layers is calculated as a dislocation vector, and this vector isdisplayed on the screen of the corresponding apparatus. Also, a warningwill be issued if the dislocation vector oversteps the dislocationtolerance that has been set beforehand. In addition, the exposuresystem, the wafer, and other targets can be evaluated by classifyingcalculated characteristic quantities according to the particulartendency and characterizing each single-shot, single-chip, or waferarea.

That is to say, according to the present invention, the microstructuredpattern inspection method for inspecting the microstructured patternsformed on the thin coating of a substrate through pattern opticalexposure is characterized in that said inspection method comprises aprocess for acquiring images of the microstructured patterns formed onsaid thin coating, a process for identifying both the shape of themicrostructured pattern on the surface of said thin coating and theshape of the microstructured pattern at the bottom of said thin coating,from said images, and a process for detecting the dislocation betweenthe two microstructured patterns that have been identified in the thirdprocess mentioned above. The shapes of the microstructured patterns canbe identified by detecting the profiles of the patterns.

For circular microstructured patterns such as contact hole patterns,misalignment between the gravity center of the circular pattern on thesurface of a thin coating and the gravity center of the circular patternat the bottom of the thin coating is detected as a dislocation. Forlinear microstructured patterns,

misalignment between the central axis of the linear pattern on thesurface of said thin coating, and the central axis of the linear patternat the bottom of said thin coating, is detected as said dislocation.

The dislocation of microstructured patterns can be visually and easilyrecognized by displaying at the patterns an arrow indicating the sizeand direction of the dislocation. It is desirable that the profiles ofthe microstructured patterns be displayed as marks such as approximatecurves or discontinuous dots.

A microstructured pattern inspection method based on the presentinvention can further comprise a process in which said dislocation isdetected at a plurality of positions within the required zone, and aprocess in which a dislocation that characterizes said zone is detectedthrough statistical processing of the dislocation at said multiplepositions. In this case, the dislocation of the entire microstructuredpatterns in the corresponding zone can be visually and easily recognizedby displaying in that zone the appropriate arrow according to theparticular size and direction of the dislocation characterizing thezone. This zone can be either a single-shot area or a single-chip area.

Since a process for comparing the distribution tendency of thedislocation at said multiple positions, and the distribution tendency ofthe dislocation estimated to occur if trouble is detected in thecorresponding microstructured pattern forming apparatus, is alsoincluded in the microstructure pattern inspection method describedabove, trouble with the microstructured pattern forming apparatus can bedetected.

In addition, according to the present invention, the microstructuredpattern inspection method for inspecting the microstructured patternsformed on the thin coating of a substrate through pattern opticalexposure is characterized in that said inspection method comprises aprocess for acquiring images of the microstructed patterns formed onsaid thin coating, a process for identifying the shapes of themicrostructured patterns from said images, and a process forcategorizing the corresponding microstructured patterns by thecharacteristic quantities of the respective shapes.

This microstructured pattern inspection method can also include aprocess in which the corresponding microstructured patterns arecategorized at a plurality of positions within a single-shot orsingle-chip area, and a process in which the categories of themicrostructured patterns characterizing said single-shot or single-chiparea are determined through statistical processing of the categorizingresults obtained at said multiple positions. During statisticalprocessing of the categorizing results, the quantity of inspectionwithin, for example, each shot or each chip, and the number ofmicrostructured patterns belonging to a specific category are comparedand the highest pattern in terms of rate is characterized as a typicalpattern at the particular position. Overall characteristics can bevisually and easily identified by displaying a single-shot orsingle-chip zone in the appropriate color according to the particularcategory of the microstructured patterns characterizing thecorresponding single-shot or single-chip area.

Under the present invention, not only the edge positions correspondingto the surface and bottom of the exposed layers of the contact holeand/or linear patterns are displayed, but also the dislocation betweenthe patterns on both layers is displayed as a dislocation vector at thesame time. And a warning will be issued if the dislocation vectoroversteps a predetermined tolerance. Thus, it becomes easy to automatethe evaluation of microstructured pattern exposure accuracy and toconfirm the exposure accuracy. In addition, not only the edge positionscorresponding to the surface and bottom of the exposed layers of thecontact hole and/or linear patterns are displayed, but also thecharacteristic quantities of exposed patterns in terms of shape arecalculated at the same time. And a warning will be issued if thesecharacteristic quantities overstep their tolerances. Thus, it becomeseasy to automate the evaluation of microstructured pattern exposureaccuracy and to confirm the exposure accuracy. In addition, it is validto analyze the dislocation vector and characteristic quantities incombined form. Furthermore, useful data for trouble detection in theoptics of the stepper, for statistical evaluation of thermal stressesdue to thermal treatment over a wide range, and for statisticalevaluation of lens aberration such as astigmatism or comatic aberration,can be collected by analyzing the distributions of the characteristicquantities of dislocation vectors and/or microstructured patterns over abroader area such as a single-chip or single-shot area or the entirewafer. And the inspection of said microstructured patterns to anymultiple processes enables collected data to be fed back to subsequentprocesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of the microstructuredinspection apparatus used for an inspection method based on the presentinvention.

FIG. 2 is an explanatory diagram showing an example of abnormal exposuredue to defects in the performance of the optics itself of the stepper.

FIG. 3 is a flowchart of dislocation vector calculation.

FIG. 4 is a diagram showing an example in which the inner and outercircles of a contact hole pattern and the corresponding dislocationvector are displayed on the screen.

FIG. 5 is a diagram showing an example of categorizing on the shapes ofcontact hole patterns.

FIG. 6 is a diagram showing an example in which a warning will bedisplayed if the major and/or minor diameter or area of the inner and/orouter circle of a contact hole pattern oversteps the correspondingtolerance.

FIG. 7 is a diagram showing an example in which the exposed surfacelayer patterns, bottom layer patterns, and dislocation vectors of linearpatterns are displayed on the screen.

FIG. 8 is a diagram showing an example of categorizing the exposedsurface layer patterns and bottom layer patterns of linear patterns.

FIG. 9 is a diagram showing an example of selecting microstructuredpatterns as samples for calculating their dislocation vectors at eachchip within a single-shot area.

FIG. 10 is a diagram showing an example of categorizing the dislocationvectors that were derived from multiple positions.

FIG. 11 is a diagram showing the tendency of microstructured patterndislocations due to lens aberration, and the tendency of microstructuredpattern deformation.

FIG. 12 is a diagram showing the tendency of a dislocation occurring ifthe projection optics is axially misaligned or has any inclined lenses.

FIG. 13 is an explanatory diagram of the linear patterns formed whendefocusing due to lens heating is occurring.

FIG. 14 shows an example of a tendency occurring with the dislocationvectors if the wafer itself is deformed or if the photoresist coating isnot uniform.

FIG. 15 is an explanatory diagram of the database structure of thedislocation vector and characteristic quantity data calculationsobtained from each pattern of a wafer.

FIG. 16 is a diagram showing an example of a screen display made for theevaluation of dislocation vectors and characteristic quantities on awafer-by-wafer basis.

FIG. 17 is a diagram showing an example of a screen display made for theevaluation of dislocation vectors and characteristic quantities on asingle-shot basis.

FIG. 18 is a diagram representing the relationship between waferdisplay, shot display, and chip display.

FIG. 19 is a flowchart explaining the entire procedure relating to amicrostructured pattern inspection method based on the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described below with referenceto the accompanying drawings. First, the methods of calculating anddisplaying the dislocation vectors with respect to the contact holepatterns and linear patterns formed on the exposed layer (photoresistcoating) of the wafer are described. Next, the method of analyzing thecauses of the dislocation by analyzing a multiplicity of dislocationvectors and deriving a general tendency is described.

FIG. 1 is a schematic diagram showing an example of a microstructuredpattern inspection apparatus designed to be used for an inspectionmethod based on the present invention. In FIG. 1, a scanning-typeelectronic microscope is shown as a typical microstructured patterninspection apparatus. Electron gun 1 provides heating filament 2 withelectroheating to obtain electron beam 8. Electron beam 8, after beingdrawn from Wehnelt units 4, is accelerated by anodes 5, then condensedthrough condensing lenses 6, and scanned by deflecting coil unit 7 towhich deflecting signals are applied from deflecting signal generator15. After that, object lenses 9 focus the electron beam on sample 11placed in samples compartment 10. Thus, electron beam 8 is scannedone-dimensionally or two-dimensionally across sample 11 on whichmicrostructured patterns are inscribed. When electron beam 8 isradiated, secondary electrons will be generated in the vicinity of thesurface of the sample 11 according to the particular shape of the sampleand these electrons will be detected by secondary electron detector 17.The secondary electrons that have thus been detected will then beamplified by amplifier 18 to become the luminance modulated signals ofCRT 14 synchronized with deflecting signal generator 15. The luminancemodulated signals will reproduce the second secondary electron imagesgenerated on the surface of sample 11 by the electron beam 8 that wasradiated in synchronization. Information on the microstructured patternsformed on the surface of the sample can be acquired using thisprocedure.

The secondary electron images displayed on CRT 14 will be picked up bycamera 13 as required.

FIG. 3 is a flowchart showing the flow of microstructured patterndislocation vector calculation based on the microstructured patternimage information that has thus being acquired. The methods of detectingand displaying dislocation vectors in the case that the microstructuredpatterns to undergo dislocation detection are contact hole patternsformed on the exposed layer (photoresist coating), are described below.In this case, although microstructured pattern images are acquired usinga scanning-type electronic microscope, these pattern images can likewisebe acquired using a means other than a scanning-type electronicmicroscope, such as an optical microscope.

First, in step 11, the microstructured pattern images that have beenacquired using a means such as a scanning-type electronic microscope,are displayed on an image display unit and then an image of any singlecontact hole pattern is specified using a mouse cursor or the like. Instep 12, polar coordinate conversions are performed on the selectedcontact hole pattern image, then a plurality of cross-sectional waveforminformation is created as profiles on a fixed-angle basis in a radialdirection from the center of the contact hole pattern, and theseprofiles are provided with various differentiation processes andthreshold value processes to derive several target edges. Among allthese target edges, only the edge corresponding to the exposed layersurface of the contact hole pattern (hereinafter, this edge is calledthe inner circle) and the edge corresponding to the exposed layer bottom(hereinafter, this edge is called the outer circle) are detected. Thefurther structural complexity and finesse of the microstructuredpatterns themselves, improvements in the performance of the inspectionapparatus to be used, and other factors are offering a more abundance interms of the edge information obtained as profiles, thereby making itmore difficult to detect the edge corresponding to the desired position.The sections corresponding to the above-mentioned outer and innercircles (edges), however, are abundant in edge information and exist atalmost a fixed distance in all angle directions from the center of thecontact hole (namely, those sections take a circular shape). Therefore,the edge corresponding to the desired position can be detected moreaccurately by deriving as more target edges as possible and thendetecting the outer and inner circles from edge information.

In step 13, the centers of gravity of the inner and outer circles thatwere detected in step 12 are derived as M1 and M2, respectively. In thisstep, although position information on the inner and outer circles isrepresented as the centers of gravity, the crossing point between themajor and minor axes of a circle, for example, can also be taken as theposition information relating to the circle. In this case, however,fixed criteria must always be used during a series of inspectionprocesses for microstructured patterns. In step 14, the vector pointingfrom the gravity center M1 of the inner circle towards the gravitycenter M2 of the outer circle is calculated as the dislocation vector ofthe contact hole. Before this calculation is made, the tolerance for thedislocation of the microstructured patterns must be set through, forexample, visually checking the image that was acquired by the inspectionapparatus. The maximum and minimum allowable vectors should beestablished as the dislocation tolerance. Likewise, tolerances shouldalso be set for the areas or major and minor diameters of the inner andouter circles, or for the area ratio between the circles. Thus, thecalculated dislocation vector is judged whether it is out of thetolerance.

As shown in FIG. 4, the inner and outer circles that have been measuredat each angle with respect to the selected contact hole are displayed onthe screen of the image display unit as the circles connecting theto-be-detected edges having the edge information corresponding to thosemeasured circles, and as the arrow connecting the dislocation vector(calculated in step 14) from M1 towards M2. In FIG. 4, although thepositive direction of the dislocation vector is shown as the directionfrom M1 to M2, the direction from M2 to M1 can also be set as thepositive direction, only if fixed criteria is always used.

During the judgment process of step 14, if the size and direction of thedislocation vector fall within the previously set tolerance, processingwill advance from step 14 to step 15 and the inner and outer circles ofthe contact hole and the dislocation vector will be displayed in whiteon the screen to indicate that the circles and the dislocation vectorstay within their tolerances. Conversely, if the size and direction ofthe dislocation vector overstep the previously set tolerance, processingwill skip to step 16 and the inner and outer circles of the contact holeand the dislocation vector will be displayed in red to warn the userthat the circles and the dislocation vector are outside theirtolerances.

In addition to or instead of the dislocation vector, the shapes of theinner and outer circles of the contact hole should be used as acriterion for judging whether the particular contact hole is anallowable hole. Typical categories relating to the shapes of the innerand outer circles include, as shown in FIG. 5, the degree of circularity(whether the circle is a true circle or an ellipsis), the ratio of themajor and minor diameters, the absolute area value, or the area ratio ofthe inner and outer circles. These shapes of the circles should becategorized either as large, medium, or small shapes, or according tothe particular ratio relative to a reference value. At the same time,tolerances on individual categories should also be established. Theshapes of the inner and outer circles of the contact hole to beinspected are compared with the respective tolerances after beinganalyzed whether the shapes belong to which of the establishedcategories.

If the shape of the contact hole oversteps the tolerance, that contacthole will be displayed in color on the image display unit as a warning.FIG. 6 shows an example in which the shape of the contact hole will bedisplayed if the tolerance is overstepped. An example of the displaymade if the outer circle is greater than its maximum allowable majordiameter is shown in FIG. 6 (a), wherein the difference from thetolerance is displayed as an arrow and the outer circle itself isdisplayed in a color meaning a warning, such as red. An example of thedisplay made if the outer circle is smaller than its minimum allowablemajor diameter is shown in FIG. 6 (b), wherein the difference from thetolerance is displayed as an arrow and the circle corresponding to theouter circle is displayed in a color meaning a warning, such as red. Anexample of the display made if the outer circle is smaller than itsminimum allowable area is shown in FIG. 6 (c), wherein the inside of theouter circle is displayed in a color meaning a warning, such as lightred. Although the examples shown in FIG. 6 are for evaluating the shapeof the outer circle of a contact hole, similar evacuations can also beperformed on the inner circle of the contact hole.

Next, the methods of detecting and displaying a dislocation vector inthe case that the microstructured patterns to be inspected are linearpatterns formed on exposed layers are described with reference beingmade to the flowcharts of FIGS. 3 and 7.

First, in step 11 of FIG. 3, images of the linear patterns to beinspected using a microstructured pattern inspection apparatus such as ascanning-type electronic microscope or optical microscope. Next, in step12, fixed detection range 21 is set, as shown in FIG. 7 (a), for theacquired linear pattern images and then as shown in FIG. 7 (b), edgesare detected within detection range 21, wherein the linear edges on thesurface and at the bottom of the exposed layer (photoresist coating).After this, processing proceeds to step 13, in which the central axes ofthe linear edges on the surface and at the bottom of the photoresistcoating are obtained at L1 and L2, respectively, as shown in FIG. 7 (b).FIG. 7 (c) is a cross-sectional view of section A-A shown in FIG. 7 (b).The perpendicular line from the center of axis L1 in detection range 21to axis L2 is recognized as the dislocation vector (L1-L2) of the linearpattern as shown in FIG. 7 (d).

In this case as well, the tolerance for the dislocation is set through,for example, visual image checks using the inspection apparatus. In step14, comparison is made between the dislocation vector that wascalculated in step 13, and the dislocation tolerance that has beenestablished beforehand. During the judgment process of step 14, if thesize of the calculated dislocation vector falls within the previouslyset tolerance, processing will skip to step 16 and the edge anddislocation vector of the linear pattern will be displayed in red as awarning. Conversely, if the size of the dislocation vector oversteps thepreviously set tolerance, processing will advance to step 15 and theedge and dislocation vector of the linear pattern will be displayed inwhite on the screen.

As with those of contact hole patterns, the shapes of linear patternscan be categorized separately for the surface and bottom each of theexposed layer (photoresist coating), and whether the particular linearpattern is an allowable pattern can be judged. Typical categoriesrelating to the shapes of linear patterns include, as shown in FIG. 8,the shape, line width, etc. of the pattern. Tolerances should also beestablished for the shapes and widths of the linear patterns so that ifa linear pattern oversteps the tolerances, that linear pattern will bedisplayed in a color, such as red, to warn the operator.

Next, the evaluation of a plurality of stepper-exposed contact hole andlinear patterns or other microstructured patterns, especially, themethod of evaluating an area equivalent to a single reticle shot or chipis described. An example of evaluating microstructured patterns usingtwo indexes . . . dislocation vector and shape . . . is shown in thisdescription.

As shown in FIG. 9, multiple chips (31 a, 31 b, 31 c, and so on),usually exist in single-shot area 30. First, a single shot of imageinformation on exposed patterns is acquired by the scanning-typeelectronic microscope or other inspection apparatus. Contact holepatterns or linear patterns are selected at multiple positions within asingle-shot area, then shape information is acquired for each pattern,and the dislocation vectors of each contact hole or linear pattern arecalculated using the method described in the flowchart of FIG. 3. Atthis time, in chips 31 a, 31 b, 31 c, and so on, of a single-shot area,sample patterns for calculating dislocation vectors at typical positionssuch as the corners (31 a to 32 d) and center (32 e) or each chip,should be selected in order to implement chip comparison as well as shotcomparison. Also, it is desirable that unless inspection throughput doesnot decrease significantly, more such sample patterns as possible shouldbe selected at equal intervals within the chip area. In addition, thesesample patterns should be acquired at the same position of each chip.

The dislocation vectors that have been calculated for each contact holepattern or linear pattern are displayed as arrows each originating from,for example, the gravity center position of the particular contact holepattern or linear pattern. If the calculated dislocation vectorsoverstep the respective tolerances, a warning will be displayed in red.With respect to these calculated dislocation vectors at each samplewithin the single-shot or single-chip area, the corresponding patternswill then be categorized as shown in FIG. 10. For the entire single-shotarea, the patterns will be categorized according to the size (large,medium, or small) of the entire dislocation vector shown in FIG. 10 (a),and according to the direction (either of about eight directions such astop, upper right, right, lower right, bottom, lower left, left, andupper left) of the entire dislocation vector shown in FIG. 10 (b).

The contact hole patterns or linear patterns are also categorizedaccording to the particular direction and dimensional deviation of eachdislocation vector that was acquired at a typical position within thesingle-shot or single-chip area. For direction, the dislocation vectorat each sample is characterized, depending on, for example, as shown inFIG. 10 (c), whether the vector points in the same direction, outward,inward, or in an irregular direction. For dimensional deviations,individual dislocation vectors are characterized, depending on, forexample, as shown in FIG. 10 (d), whether the patterns are equal, largeonly at edges, large only in the center of the reticle, or large in aspecific position only. Each characteristic quantity is linked to thearea from which the particular characteristics have been extracted. Themethods of categorizing patterns are not limited to the four types shownin FIG. 10; other characteristic quantities can be used instead,provided that they represent the tendencies of the dislocation vectorswithin the single-shot area.

The dislocation vectors representing the entire single-shot orsingle-chip area are calculated as follows:

In the “k”th area of chips, for example, a contact hole pattern of one“k” chip and a linear pattern of two “k” chips are set as samplepatterns for the calculation of the corresponding dislocation vectors,and each chip is provided with such processing as described in theflowchart of FIG. 3. When the dislocation vectors that have thus beencalculated for the contact hole pattern are taken as SH₁, SH₂, and so onup to SH_(k1), and the calculated dislocation vectors of the linearpattern are taken as Sl₁, SL₂, and so on up to SL_(k2), dislocationvector VC_(k) representing the chip can be calculated using expression 1below. If each pattern differs in design specifications, since the sizesof the dislocation vectors calculated will also differ, adjustments willbe performed using coefficients α and β. The dislocation vectorsrepresenting each shot area can also be calculated similarly.$\begin{matrix}{\overset{\longrightarrow}{{VC}_{k}} = {{\sum\limits_{i = 1}^{k1}{\alpha_{i}\overset{\longrightarrow}{{SH}_{i}}}} + {\sum\limits_{j = 1}^{k2}{\beta_{j}\overset{\longrightarrow}{{SL}_{i}}}}}} & \left\lbrack {{Expression}\quad 1} \right\rbrack\end{matrix}$

After the contact hole and linear patterns have been categorized bytheir shapes as shown in FIG. 5 or 6, the results are statisticallyprocessed in the single-shot or single-chip range, and for example, thelargest value in terms of the number of categories is taken as a typicalvalue of the shape relating to the corresponding area.

The occurrence of some abnormality caused by the four factors describedearlier in this SPECIFICATION can be estimated by characterizationrelation to the thus-calculated sizes and distributions of thedislocation vectors within a single-shot area, and from categorizingresults on the shapes of the contact hole or linear patterns.

FIG. 11 shows the tendency of dislocation vectors occurring in asingle-shot area when lens aberration is detected in the patternprojection optics. For example, if, as shown in FIG. 11 (a), thedislocation vector points in a radially inward direction from the centerof the reticle within a single-shot area, or if the contact hole isdeformed into either a vertically long shape towards the center of thereticle as shown in FIG. 11 (b), or a horizontally long shape towardsthe center of the reticle as shown in FIG. 11 (c), such abnormality islikely to be due to lens aberration in the stepper. If thesecharacteristics are detected, therefore, a warning implying theoccurrence of lens aberration in the projection optics of the stepperwill be displayed along with images of the corresponding pattern.

FIG. 12 shows the tendency of dislocation vectors occurring when theprojection optics is axially misaligned or has an inclined lenses. If,as shown in FIG. 12, multiple dislocation vectors within a single-shotarea point in the same direction, this implies abnormality due to axialmisalignment of the projection optics. If these characteristics aredetected, therefore, a warning will be issued by, for example,displaying a message indicating the abnormality.

FIG. 13 is an explanatory diagram of the linear patterns formed whendefocusing due to lens heating is occurring. The linear pattern formedwhen the best focus is obtained, is shown in FIG. 13 (a), and the linearpatterns formed during defocusing are shown in FIGS. 13 (b) and (c).Shown at the left of FIGS. 13 (a), (b), (c) each are top views of thelinear pattern, and shown at right are cross-sectional epitomic views ofthe linear pattern. FIG. 13 (b) shows a linear pattern whose defocusingdirection is plus (this indicates that the focal position is above theexposed surface), and this linear pattern has a thin top and is thickeras it goes downward. FIG. 13 (c) shows a linear pattern whose defocusingdirection is minus (this indicates that the focal position is below theexposed surface), and this linear pattern has a thin top and a flared,indistinct bottom. Since these patterns having a thin top and/or athick/indistinct bottom are likely to be due to defocusing, a warning isdisplayed to imply the occurrence of the abnormality. Lens heating iscaused by the accumulation of heat inside, and on the surfaces of the,lenses due to continued exposure for a long time. Characteristics on the“lens heating” event of the lenses to be used can be understood byexamining chronological changes in the shape of the pattern.

FIG. 14 shows an example of a tendency occurring with the dislocationvectors if the wafer itself if deformed or if the photoresist coating isnot uniform. Warped or deflected wafer or nonuniform photoresist coatingaffects the axial misalignment of the entire wafer significantly.Factors due to defects in wafer status, however, can be evaluated bycalculating dislocation vectors with respect to each chip within eachwafer and examining their tendencies. As briefly shown in FIG. 14,abnormality due to either defects in the status of the wafer itself ornonuniform photoresist coating, is usually distributed in one specificarea of wafer 30. Therefore, the occurrence of abnormality due to eitherdefects in the status of the wafer itself or nonuniform photoresistcoating, can be estimated by concentrating attention on such specificcharacteristics and analyzing their distributions within the wafer area.

The method of displaying information on the dislocation vectors andshapes of microstructured patterns such as contact hole and linearpatterns, is described next. One or more areas are specified for eachchip in each wafer area, and any discoloration vectors in the specifiedarea(s) are calculated. Also, dislocation vectors for each chip or eachshot are characterized using a similar method [Expression 1] shownabove. When information on the dislocations of microstructured patternsis displayed, either a view showing the wafer when it is partitionedinto shot areas, or a view showing a specific shot area when it ispartitioned into chip areas is displayed on the screen of the displayunit first and then the dislocation vectors that were calculated foreach shot area of the wafer or for each chip area in a specific shot aredisplayed in color. As with the processing sequence shown in theflowchart of FIG. 3, if the dislocation vectors overstep the respectivetolerances for each shot or each chip, a warning will be issued bydisplaying the vectors in a conspicuous color such as red.

FIG. 15 is an explanatory diagram of the saving format of thedislocation vector and characteristic quantity data calculationsobtained from each pattern of a wafer. The data is of the tree structurehaving a hierarchy covering the wafer, shots, chips, and in-chippatterns. Each in-chip pattern record has pattern's x- andy-coordinates, pattern information (whether the pattern has a linearshape or a contact hole shape), the size and direction of thedislocation vector of the corresponding pattern, shape information, andother characteristic quantities. On a chip-by-chip basis, the average ofvarious information on the pattern belonging to the chip is retained asa record of that chip. Likewise, on a shot-by-shot basis, the average ofvarious information on the chip corresponding to the shot is retained asa record. Also, each value retains as its “parents” the ID of the areaof the immediately upper hierarchical level, as its “brother” the ID ofan area derived from that parent, and as its “child” the ID of theimmediately lower hierarchical level of direct lineage. Chip “3”, forexample, retains “1” as its parent, “4” as its brother, and “7” and “8”as its children.

Examples in which the dislocation vector characteristic quantities thathave been acquired using the method described above are statisticallyprocessed and displayed on the screen, are shown in FIGS. 16 and 17. Thedisplay shown in FIG. 16 relates to the corresponding wafer, and thedisplay in FIG. 17 is for the corresponding shot range.

As shown in FIG. 16, wafer display mode displays information on ashot-by-shot basis. On the wafer map, each shot area is partitioned by ashape such as a square, and the characteristic quantity and dislocationvector of each entire shot area are displayed. A specific number from 1to 16 is assigned to each shot area, with the number corresponding tothe coordinates within the wafer. Each shot area from 1 to 16 on thewafer map is displayed properly in color coded form according to thecharacteristic quantity representing the shot (the greatestcharacteristic quantity in the shot: A, B, C, or, D). Also, thedislocation vector representing the shot area is displayed in overlappedform on that shot area. The distribution of characteristic quantities onthe shape of the microstructured pattern is digitally displayed in thetable at the bottom of the display. Numerals in this table denote thenumber of times each characteristic quantity appeared in each shot area.At the right end of the table is displayed the total number of timeseach characteristic quantity appeared in the entire shot range, and ifthis appearance tendency shows any characteristics, thesecharacteristics will be displayed under “Evaluation”. When a typicaltendency is analyzed beforehand and actual evaluations apply to thattendency, explanatory statements on further detailed analyses on thetendency will be displayed with “(1)” or “(2)” at the bottom of thescreen display.

As shown in FIG. 17, chip display mode displays information on achip-by-chip basis. In shot display mode, a map of the wafer is alsodisplayed at the same time to indicate to what position on the wafer mapthe current shot corresponds. Each chip from 1 to 8 within the shot isdisplayed properly in color coded form according to the characteristicquantity representing the chip (the greatest characteristic quantity inthe chip: A, B, C, or D). Also, the dislocation vector representing thechip is displayed in overlapped form on that chip. The distribution ofcharacteristic quantities on the shape of the microstructured pattern isdigitally displayed in the table at the bottom of the display. At theright end of the table is displayed the total number of times eachcharacteristic quantity appeared, and if this appearance tendency showsany characteristics, these characteristics will be displayed under“Evaluation”. When a typical tendency is analyzed beforehand and actualevaluations apply to that tendency, explanatory statements on furtherdetailed analyses on the tendency will be displayed with “(1)” or “(2)”at the bottom of the screen display. In the example of FIG. 17,“Abnormal” is shown as the evaluation of characteristic quantity B, andthe column of chip 1 is displayed in light red.

The display shown in FIG. 16 or 17 changes according to thecharacteristic quantity to which attention is to be given (the layout ofthe display remains the same). For example, if this characteristicquantity is “A: Characteristics of the circle” as shown at the top ofFIG. 5, the characters “True circle”, “Vertically long”, “Horizontallylong”, “Oblique (1)”, and “Oblique (2)”, are assigned to the items ofcharacteristic quantities A, B, C, C, and E, respectively, in FIG. 16 or17. When five categories are present, the number of items is also five(from A to E) and five different colors are assigned as display colors.The display of each shot or chip area is coded in the colorcorresponding to the characteristic quantity representing the area.Also, “Characteristic quantity” in the table functions as a button, andwith each press of this button, the categorizing basis in FIG. 5 changesto “Characteristics of the circle” first and then “Ellipticity”, “Area”,and so on, in that order. As “Characteristic quantity” changes in thisway, the numeric data in the table and the display color of the shotarea within the wafer map or of the chip area within the shot will alsocorrespondingly change.

Although it is not shown in the corresponding FIG., display mode for asingle-chip range is also provided. This display mode for a single-chiprange is very similar to the display mode for a single-shot range, andin the single-chip display mode, any dislocation vectors of the samplepatterns within one chip are displayed at the patterns. The shot displayalso appears at the same time so that the position of the current chipin the shot can be readily identified.

FIG. 18 shows the relationship between wafer display, shot display, andchip display. In the wafer display mode shown in FIG. 18 (a), forexample, if the operator clicks in shot area 2 on the display with alarge dislocation vector, the current display will change to the shotdisplay mode to display that shot in enlarged form as shown in FIG. 18(b). Average dislocation vectors on each chip of the shot are displayedin the shot display mode, and in this mode, if the operator clicks atchip 7 on the display with a large dislocation vector, that chip will bedisplayed in enlarged form and the distribution of dislocation vectorsin the chip will also be displayed, as shown in FIG. 18 (c). Thus, theposition with a significant dislocation vector can be detected. It isalso possible to move control to the shot display mode bydouble-clicking on the shot display, and to return control to theoriginal shot display mode by double-clicking on the chip display. Thedatabase structure shown in FIG. 15 is used during movement from thewafer display mode to the shot display mode, or vice versa. For example,when control is moved from the display of shot 1 to that of a chip, thecorresponding chip display is created using the information of chips 3and 4.

FIG. 19 is a flowchart explaining the entire procedure relating tomicrostructured pattern inspection based on the present invention.First, in step 21, the wafer to be inspected is loaded into aninspection apparatus such as a scanning-type electronic microscope oroptical microscope. Next, in step 22, the shot (or chip) to be inspectedfor dislocation vector or geometrical characteristics of themicrostructured pattern is specified, and processing further advances tostep 23, wherein the dislocation vector calculating position in the shot(or chip) is then specified.

Next, in steps 24 to 28, dislocation vector calculation andcharacterization are executed for the specified microstructured pattern.In step 29, the calculated dislocation vector or the characteristicquantity of shape is judged whether the corresponding tolerance isoverstepped, and if the tolerance is not overstepped, processing willproceed to step 30, wherein the dislocation vector or themicrostructured pattern will then be displayed in normal color.Conversely, if the tolerance is overstepped, processing will skip tostep 31, wherein the dislocation vector or the microstructured patternwill then be displayed in red as a warning.

Processing will proceed to step 32, wherein characteristic tendencies oneither the distribution of the dislocation vectors that were calculatedin steps 24 to 28, or the shape of the specified microstructured patternwill then be statistically analyzed. Processing will further proceed tostep 33, wherein judgment will be made whether the tendency ofcharacteristic qualities that was analyzed in step 32 will implyabnormality about the stepper or wafer. In the judgment process of step33, a combination of, for example, such dislocation vector distributionpatterns as shown in FIGS. 11 (a), 12, and 14, and the known causes ofthe abnormality, or a combination of such pattern shape-relatedcharacteristic quantity distribution patterns as shown in FIGS. 11 (b),11 (c), and 13, and the known causes of the abnormality, is retained asa table, and the tendency of the characteristic quantities that werecalculated in step 32 is checked against the table to search for theactual cause of the abnormality. If the distribution pattern of thedislocation vectors or the distribution of the shape-relatedcharacteristic quantities of the microstructured pattern exists in thetable and implies abnormality about the stepper or wafer, processingwill advance to step 34 and a warning message on the cause of theabnormality will be displayed.

According to the present invention, microstructured pattern exposureaccuracy can be automatically evaluated and easily confirmed. Also,trouble in the optics of the stepper or in the wafer can be detected byevaluating the distributions of the characteristics of microstructuredpatterns over a broader area such as a single-chip or single-shot areaor the entire wafer.

1. A pattern inspection method for inspecting a pattern formed in a chipof a semiconductor wafer containing a plurality of chips, comprising:forming a pattern image of each chip of the semiconductor wafer, or ofan area shot by an optical exposure apparatus, on the semiconductorwafer, with a scanning electron microscope; detecting a deviationbetween a surface and a bottom of a pattern for each chip or for thearea shot by the optical exposure apparatus based on the image; anddisplaying information regarding the deviation between the surface andthe bottom, for each chip or area shot by the optical exposureapparatus, on a wafer map.